Antibodies are commonly used to functionalize nano-devices and nano-objects for detection of specific biomarkers. Such antibody-based molecular recognition has limited capability for field-deployable or point-of-care modalities, as antibodies need a certain range of temperatures, humidity, and solution conditions to retain their structure. In terms of the solution conditions, an important parameter is the need for low ionic strength. Low ionic strength of the buffer solutions is needed to overcome surface Debye screening, but it also results in weak interactions between the surface probe and solution target.
There are other means of protein detection, including amperometric and optical detection, such as those employing microarray technology. Electrical detection methods include capacitive, impedometric, and voltametric detection. In the case of optical detection, a fluorescent tag is usually attached to the DNA or the protein and the change in fluorescent intensity is measured after binding. However, the tagging of the DNA or protein molecule can change the thermodynamic properties of the molecular interactions of DNA and, in some cases, unnaturally stabilize or destabilize the DNA double-strand of the DNA or protein and change the melting temperature significantly. Additionally, expensive fluorescent microscopes are needed to visualize the data and normalization of the data to references remains problematic. Further, the hybridization of the probe and target molecules is a diffusion-limited process requiring long-incubation times as the target molecules must travel to the arrayed probes on the surface of the chip. The fluorophores are also known to have great effect on the stability of the duplexes as a function of the sequence itself. In addition, fluorescent dyes photobleach, quench statically, or interact with each other, so the microarray technologists need to have very detailed knowledge about the limitations of the optics, reagents used, and the sample interactions.
Thus, there is a need for biosensors for proteins and cells, including cancer cells, that integrate sensing, characterization, comparative analysis and decision making all on-board a single chip, while sustaining or increasing sensitivity and specificity. The invention is directed to these, as well as other, important ends.